In a conventional wet sump internal combustion engine, a baffle plate is provided in an upper part of an oil pan, and a bottom portion of the baffle plate is provided with a laterally elongated through hole. A slat extends from a downstream edge of the through hole toward the upstream side. See JP3552414B. This baffle plate allows the lubricating oil that is deposited on the upper surface of the baffle plate to be expelled to the oil reservoir in the oil pan via the through hole of the baffle plate by using the air flow created by the rotation of the crankshaft. However, this air flow impinges directly upon the surface of the oil in the oil reservoir via the through hole so that the oil may be aerated.
JP4016932B proposes to provide a through hole in a part of the baffle plate offset from the center thereof with an aim to avoid such an aeration.
However, the arrangement proposed by JP4016932B has the drawback that the oil cannot be expelled to the oil reservoir as promptly as desired.